Interlocked waveguide assembly

ABSTRACT

A self-aligned waveguide assembly is constructed of interlocked sections of hollow rectangular waveguide which are abutted end to end. The abutted ends of the sections are interlocked by dovetailing the sections along the broad walls of the waveguide in a manner insuring alignment of the broad walls. One of the mated sections has locating tabs extending from its narrow walls. The tabs overlap the narrow walls of the adjacent interlocked section and maintain the narrow walls in alignment by preventing slippage along the dovetail joint. Channels in the interlocks are provided which permit solder to have access to the interface between the abutted ends completely around the joint.

Stts l 111 [72] Inventor Joseph 1F. lBaldelll Marlboro, lllass. [21] AppLNo. 8783M [22] Filed Nov. 20, 11969 [45] Patented Aug. 3, 19711 [73] Assignee Microwave Development Laboratories,

inc, Needham Heights, Mass.

[54] INTERILOCKEID WAVEGUE ASSEMBLY 5 Claims, l0 Drawing Fm.

[52] [1.5. Cl 285/287, 138/155, 285/297, 285/325, 285/330, 333/98 [51] Int.Cl lFllSl 113/08 [50] Field olSearclt 138/155, 171; 285/294, 297, 325, 330, 424, 21, 22, 287, 329; 333/95, 98; 29/509, 600

[56] Kellen-enema Cited UNITED STATES PATENTS 1,916,930 7/1933 Lyness 285/325 X 3,149,295 9/1964 Grebe 3,452,306 6/1969 Walker ABSTIRNCT: A self-aligned waveguide assembly is constructed of interlocked sections of hollow rectangular waveguide which are abutted end to end. The abutted ends of the sections are interlocked by dovetailing the sections along the broad walls of the waveguide in a manner insuring align ment of the broad walls. One of the mated sections has locating tabs extending from its narrow walls. The tabs overlap the narrow walls of the adjacent interlocked section and maintain the narrow walls in alignment by preventing slippage along the dovetail joint. Channels in the interlocks are provided which permit solder to have access to the interface between the abutted ends completely around the joint.

PATENTEU AUG 3 IBYI SHEU 1 0F 2 INVENTOR JOSEPH F BALDELL! ATTORNEY WWI-2m sun 3596'. 93?

- SHEET 2 [IF 2 INVENTOR JOSEPH F. BALDEL Ll ATTORNEY INTIETTLGUIKEID WAVEGUIDE fliSblEMllhIfl! DISCUSSION OF THE PRIOR ART Hollow metal pipe of rectangular cross section is the predominant type of waveguide now in use for the guided transmission of electromagnetic waves. It is common to assemble rectangular waveguide transmission lines from aligned sections that are rigidly joined end to end. In joining contiguous ends of the sections, the primary objective is to make a joint that offers no appreciable discontinuity to the flow of wave energy. In some waveguide systems, the system is pressurized and the joints must, in addition to providing electrical continuity, be free of leaks and capable of containing the pressurized medium. Although electronic apparatus is usually designed to avoid placing appreciable mechanical loads on the waveguide, nevertheless the mechanical strength of a waveguide joint is not an unimportant factor as unexpectedly high loads have, on occasion, been known to be imposed upon the guide.

The losses and reflections from a joint between two sections of waveguide pipe arranged end to end are negligible if care is taken to align the sections and to obtain good electrical continuity between the abutting end surfaces. To provide such a joint, it has been conventional to make the facing ends of the sections flat and parallel, to butt the ends together, and to join them by solder while the sections are held in alignment by a core inserted into the pipes. The core precisely fits the rectangular apertures in the waveguide sections and, in addition to maintaining those sections accurately aligned, prevents the solder, which is free flowing, from forming a bead in the interior of the waveguide. It has also been conventional to form a joint between abutting flat ends of waveguide sections by placing an external sleeve around the sections. The sleeve maintains the sections in alignment (without requiring a core) and a groove in the sleeve holds the supply of solder that surrounds the joint. The solder is of a type that is not too free flowing when molten and thus does not form a bead in the interior of the waveguide when the sleeve is heated to sea] the joint.

The internal core method of holding the sections in alignment does not readily lend itself to assemblies in which one or both of the sections being joined are curved. The joint formed by the internal core method or by the extemal sleeve method tends to be mechanically weak because the strength of its union depends upon the solder at the joint. Solder, as is well known, is a relatively weak material and is markedly inferior in strength to the metal walls of the waveguide. Further, neither the internal core method nor the external sleeve method are suited to the rapid assembly of waveguide sections. An internal core or an external sleeve is suitable for only one size of waveguide and a multitude of such cores and sleeves are required for the various sizes in which rectangular waveguide is available.

THE INVENTION The primary objective of this invention is to provide a waveguide assembly in which the joined components are interlocked to insure accurate alignment of the sections while providing a mechanically strong union which permits solder to enter the interface between the mated sections. The invention resides in interlocking the sections along their broad walls by a dovetail joint and providing one of the sections with lateral tabs which overlap the narrow walls of the adjacent section to prevent endwise movement of that section. The dovetail joint assures alignment of the broad walls of the mated sections while the lateral tabs assure alignment of the narrow walls. Each broad wall joint has a longitudinally extending solder channel which communicates with the interface between the abutted ends along substantially the entire length of the broad wall. The channel conduces to the entry of solder in the interface region whereby the solder makes an electrically continuous path across the joint.

The invention can be better understood from the following exposition when considered in conjunction with the accompanying drawings in which:

FIG. ll depicts an embodiment of the invention having a straight waveguide section joined to a bent section of waveguide;

FIG. 2 is a sectional view in elevation taken along the parting plane 2-2 in FIG. 1',

FIG. 3 shows a horizontal section "through the FIG. 1 embodiment taken along the plane 3-3;

FIG. 4 is an enlarged view showing the chamfered edge on one of the interlocking sections;

FIG. 5 is an enlarged sectional view showing the provision of a solder channel along the narrow wall joint;

FIG. 6 is a top plan view of a waveguide pipe having horizontally extending tabs;

FIG. 7 is a sectional view taken along the parting plane 7-7 in FIG. 6;

FIG. b is a sectional view taken along the parting plane 8-3 in FIG. 6 and depicts the horizontally protruding tabs;

FIG. 9 depicts a waveguide component in which one tab is initially formed in the vertical position and the other tab is initially at the horizontal; and

FIG. I0 depicts a modified form of interlocked joint.

THE EXFOSITION An embodiment of the invention is shown in FIG. I wherein the waveguide assembly, by way of example, consists of a straight section I of hollow rectangular metallic waveguide joined to a hollow rectangular metallic bent section 2. The two components of the assembly, as indicated in the cross-sectional view of FIG. 2, have their contiguous ends abutted and interlocked. The straight section, as its mated end, has its upper broad wall 11A and its lower broad wall llB held in engagement with the corresponding broad walls 2A and 2B of the bent section by interlocked joints D11 and D2 which form a dovetail connection. The interlocked joints act to align the upper and lower broad walls while forming a mechanically strong union between the sections. In waveguide, for the shorter wavelengths, the walls are relatively thin and the cutting of dovetailing grooves in the upper and lower broad walls tends to weaken those walls. Further, the straight section of hollow rectangular metallic waveguide is usually an extrusion which makes it impractical, for economic reasons, to depart from a uniform wall thickness. The reduction in thickness caused by cutting dovetail grooves in the broad walls of the straight waveguide is, therefore, preferably held to a minimum to avoid unduly weakening these walls.

To obtain a mechanically strongjoint, one of the sections, in this instance the bent section 2, has a lip 3 on its upper broad wall and a lip d on its lower broad wall into which dovetailing grooves are cut. The lip, in effect, increases the thickness of the broad wall at the mating end of the bent section and through an appreciable amount of metal is removed to provide the dovetail groove, the wall thickness, even at its thinnest point is adequate to insure a mechanically strong joint. The interlocked joints DI and D2 are constructed by conventional metal cutting techniques to assure the accurate alignment of the inner surfaces of the upper and lower broad walls of the waveguide sections.

To prevent the sections from sliding relative to one another and to insure the accurate alignment of the narrow walls of the two sections, one of the sections is provided with lateral tabs which overlap the narrow walls of the adjacent section. It is convenient to have the lateral tabs and the lips on the bent section because that section can be readily cast or fabricated with those appendages whereas the straight section is usually an extrusion which is difficult to alter. In FIG. 3, the tabs 5 and ti are integral with the narrow walls 2C, 2D of the bent section 3 and overlap the narrow walls llC, ID of the straight waveguide section. The straight waveguide section 1 is, therefore, laterally confined between tabs 5, 6 and is prevented by those tabs from endwise movement in either direction. Thus, the tabs prevent the sections from sliding along the dovetail joint.

With the two waveguide sections assembled, the joints are soldered to form a permanent connection having excellent electrical conductivity thereacross. To insure the solder flowing into the interface between the abutted ends, a channel is provided in each interlocked joint D1 and D2 along the entire length of the broad wall. Preferably, the channel is formed, as shown in FIG. 4, by chamfering the edge I] of the mating section. In FIG. 2, the channel in joint D1 is indicated by S1 and the channel in joint D2 is indicated by S2. The tabs and 6 are arranged so that they do not obstruct the flow of solder into the channels. Preferably the tabs are relieved to uncover the ends of the channels. Molten solder is drawn into the channel by capillary action an solidly fills the channel along its entire length. From the channel, the molten solder flows into the interface between the abutted ends of the joint and solidly unites the two sections.

Topromote the flow of solder along the lateral tabs, the edges of the narrow walls 1C and 1D can be chamfered to form solder channels as indicated by the chamfered edge of wall 1C in FIG. 5 which forms channel S3. Such a channel is preferably provided where the tab has a sharp right angled corner which causes the tab to lie flat against the adjoining section.

In one embodiment of the invention, the tabs 5 and 6 are formed, as shown in FIGS. 7 and 8, on the end of the waveguide section having the lips 3 and 4. Initially, the tabs 5 and 6 extends transversely to the narrow waveguide walls and the tabs are subsequently bent into the positions depicted in FIG. 3. It has been found that when a tab is made in this manner it may not be necessary to chamfer the edge of the mating section as in FIG. 5 because a gap is usually present into which the solder is drawn along the entire length of the tab by capillary action.

As an alternative to having both tabs initially extend horizontally as depicted in FIG. 8, one of the tabs is initially formed in the vertical position as indicated by the tab 7 in FIG. 9. The tab 7 acts as a lateral position locator to insure that when the two sections of waveguide are assembled, the narrow walls are in proper alignment. The tab 6, when bent to the vertical, locks the two sections in alignment by preventing lateral movement of one section relative to the other.

In FIG. 2, lips 3 and 4 are depicted as having V-shaped edges engaged with V-shaped grooves in the broad walls 1A and 1B of the mating section. By employing the buttress shape depicted in FIG. 10, the grooves in the broad walls can be somewhat shallower without diminishing the mechanical strength of the joint. In the buttress shape, the sharply pointed end of the V is removed from the lip 8 to provide a truncated V and the cooperating groove in the broad wall is cor- 'rcspondingly shaped with a flat bottom. A solder channel S4 is formed by chamfering the edge of the buttress-shaped tooth 9 with which the lip 3 is engaged. The channel S4 ensures that solder will flow into the interface between the abutted ends of the two mated sections along the entire extent of the broad wall.

It would be an obvious change to lock the sections together by dovetailing the narrow walls rather than the broad walls and to place the locating tabs on the broad walls. However, as between the two arrangements, greater mechanical strength is obtained by dovetailing the broad walls and therefore that arrangement is preferred.

Because the invention may be embodied in varied structures, it is not intended that the patent be limited to the forms here illustrated or described. Rather, it is intended that the patent be construed to embrace those waveguide assemblages which utilize the invention defined in the appended claims and include assemblages which are mere obvious equivalents of the invention defined in the appended claims.

I claim: l. A waveguide assembly comprising interlocked sections of hollow rectangular waveguide abutted end to end, the mated ends of the sections having cooperating means along the broad walls which form a dovetail joint between the sections, one of the sections having locating tabs extending from its narrow walls and overlapping the adjacent narrow walls of the mated section, and each broad wall joint having a solder channel extending along its entire length, the solder channel communicating with the interface between the abutted ends along the entire extent of the broad wall joint.

2. The waveguide assembly according to claim 1, wherein the cooperating means includes a lip on each broad wall of one section, each lip overlapping the adjacent broad wall of the mating section and protruding into a groove in the adjacent broad wall. 3. The waveguide assembly according to claim 2, wherein the solder channel is formed by a chamfer on the broad wall edge of one of the mated sections. 4. The waveguide assembly according to claim 3, wherein each locating tab extends along substantially the entire width of the overlapped narrow wall, and each narrow wall joint has a solder channel along the entire extent of the tab, the solder channel communicating with the interface between the abutted ends along the entire length of the tab. 5. The waveguide assembly according to claim 4, wherein the edge of the narrow wall covered by the overlapping tab is chamfered to provide the solder channel. 

1. A waveguide assembly comprising interlocked sections of hollow rectangular waveguide abutted end to end, the mated ends of the sections having cooperating means along the broad walls which form a dovetail joint between the sections, one of the sections having locating tabs extending from its narrow walls and overlapping the adjacent narrow walls of the mated section, and each broad wall joint having a solder channel extending along its entire length, the solder channel communicating with the interface between the abutted ends along the entire extent of the broad wall joint.
 2. The waveguide assembly according to claim 1, wherein the cooperating means includes a lip on each broad wall of one section, each lip overlapping the adjacent broad wall of the mating section and protruding into a groove in the adjacent broad wall.
 3. The waveguide assembly according to claim 2, wherein the solder channel is formed by a chamfer on the broad wall edge of one of the mated sections.
 4. The waveguide assembly according to claim 3, wherein each locating tab extends along substantially the entire width of the overlapped narrow wall, and each narrow wall joint has a solder channel along the entire extent of the tab, the solder channel communicating with the interface between the abutted ends along the entire length of the tab.
 5. The waveguide assembly according to claim 4, wherein the edge of the narrow wall covered by the overlapping tab is chamfered to provide the solder channel. 